In vehicles known from the prior art, transmission devices are arranged between a power aggregate and a drive output, in order to enable various operating conditions such as driving forward, driving in reverse and thrust and traction operation. During this, the drive torque of the engine is applied to the front axle in front-wheel-drive vehicles, to the rear axle in rear-wheel-drive vehicles, and in the case of all-wheel-drive vehicles to two or more of the axles of the all-wheel-drive vehicle with various set degrees of distribution.
In such vehicles, a main transmission is arranged between the drive engine and the driven vehicle axles by way of which various gear ratios can be engaged. This takes into account the manner in which a drive engine made as an internal combustion engine delivers its torque or power as a function of speed. Such main transmissions are made as manual shift transmissions, sequential automatic transmissions or even continuously variable automatic transmissions.
To be able to distribute the torque delivered by the power aggregate to several driven vehicle axles in the longitudinal direction of a vehicle, in the power flow of a drive train transmission devices or longitudinal distributor transmissions are connected downstream from the main transmission described above. These being designed as separate structural units, being integrated in the main transmission or being made as so-termed hang-on systems on the main transmission.
Furthermore, provision is also made for distributing the drive torque delivered to a driven vehicle axle between the two drive wheels of that vehicle axle so that the drive wheels of a driven vehicle axle can be driven at different speeds independently of one another in accordance with the different path lengths of the left and right steering tracks, whereby the drive torque can be distributed to the two drive wheels symmetrically and thus free of any yaw torque component.
The structural type of differentials conventionally used in practice are so-termed bevel gear differentials, spur gear differentials of planetary design or even worm gear differentials. Spur gear differentials, in particular, are mostly used as longitudinal differentials because of the possibility of unsymmetrical torque distribution. At present, bevel gear differentials are standard for transverse equalization in vehicles and worm gear differentials are used both for longitudinal and for transverse distribution.
However, these two advantages are offset by the drawback that because of the equalizing action of a differential, the propulsive forces that can be transferred to the road by two drive wheels of a vehicle axle or from two or more driving axles is determined in each case by the lower or lowest transferable drive torque of the two drive wheels or driving axles. This means that when, for example, a drive wheel resting on smooth ice skids, no torque higher than that of the skidding drive wheel can be supplied to the other drive wheel, even when the latter is on ground that it could grip. In such a driving situation, the vehicle might disadvantageously not be able to start off because of the equalizing action of a differential, which allows a difference of speed between two drive output shafts of the differential.
Accordingly in practice, it has become customary to prevent equalization movement of a differential by suitable means in the event of critical driving situations. This is done, for example, by a differential lock, known as such, which can be actuated manually or automatically by mechanical, magnetic, pneumatic or hydraulic means and which fully prevents any equalization movement by blocking the differential.
WO 02/09966 A1 discloses a transmission for a four-wheel-drive vehicle, in which an input shaft is connected to a planetary gearset. Here, the planetary gearset is made as a three-shaft planetary gearset, such that an annular gear wheel is in active connection with the input shaft, a solar gear wheel with a first drive output shaft and the planetary carrier with a planetary gear system and with another drive output shaft of the transmission. The planetary gear system comprises three solar gear wheels and three planetary gears each of which meshes with one of the solar gear wheels, which are made integrally with one another and have a common planetary carrier. The planetary carrier of the planetary gear system and one of its solar gear wheels are each in active connection with a brake. These brakes are connected to a force supply and are operated independently of one another and controlled by an electronic control device. A plurality of sensors are connected to the electronic control device, whose signals are received by the electronic control device and converted into corresponding control signals for the two clutches. Depending on the control of the two clutches, the initial speed and the torque transmitted to the front axle, and the drive output speed of the planetary gear system and the torque transmitted to the rear axle, are adjusted.
However, these all-wheel distributor systems known from the prior art have the drawbacks that variable distribution of the torque can only be carried out to a limited extent and that they are of elaborate design. Owing to their elaborate structure, such all-wheel distributor systems have large overall dimensions and, therefore, take up considerable space. Furthermore, the known all-wheel distributor systems are disadvantageously characterized by large inherent weight and high manufacturing costs.
Accordingly, the purpose of the present invention is to make a transmission device for a drive train of a vehicle available, which is of simple construction and can be manufactured inexpensively, and a method for controlling a transmission device with which the degree of distribution of a drive torque between two drive output shafts can be varied according to need.